Solvent extraction from biodegradable microparticles

ABSTRACT

Embodiments may also include a system for reducing a solvent concentration in a plurality of microparticles. The system may include a solvent extraction tank. In the solvent extraction tank, a mixture including the plurality of microparticles and the solvent may be contacted with water to form an aqueous suspension. A first portion of the solvent may dissolve into the water of the aqueous suspension to reduce the solvent concentration in the plurality of microparticles. The system may also include a concentration unit in fluid communication with the solvent extraction tank. The concentration unit may further reduce the solvent concentration in the plurality of microparticles. A microparticle concentrate may be formed. The system may further include a washing unit. In the washing unit, the microparticle concentrate may be contacted with a washing solution and may form an amalgam of washed particles.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/974,201, filed Dec. 18, 2015, which is a divisional of U.S. patentapplication Ser. No. 14/324,734, filed Jul. 7, 2014, now U.S. Pat. No.9,439,864 issued Sep. 13, 2016, the disclosures of which are herebyincorporated by reference in their entireties for all purposes.

BACKGROUND

Biodegradable microparticles may be used to deliver drugs, hormones,proteins, and other medically active agents to a patient. As theydegrade, the microparticles may gradually release agents to the bodyintravenously or subcutaneously and may be administered to the body witha needle. Biodegradable microparticles may reduce the frequency ofinjections, as the agents are released gradually into the body. Themicroparticle size distribution and flowability characteristics affectthe gauge and other characteristics of the needle. More flowablemicroparticles may be easier to fill into vials and may be more easilyinjected with a large gauge (smaller diameter) needle. Once in the body,the rate of release and the concentration of the medically active agentmay be related to the microparticle size, the microparticle sizedistribution, the initial concentration of the medically active agent,and other characteristics of the microparticles. Such biodegradablemicroparticles also need to meet health and safety regulations forcontaminant concentrations including the solvents used to prepare themicroparticles. Thus, a need for microparticles with superiorsyringability, injectability, flowability, uniformity, and puritycharacteristics exists. The methods and systems described herein providesolutions to these and other needs.

BRIEF SUMMARY

Solvents are often used during the preparation of biodegradablemicroparticles. Initially, these solvents are at concentrations that arehigher than levels safe for injection into a patient. The solventconcentration in the microparticles can be reduced by extracting thesolvent with a liquid, such as water. The solvent extraction may besplit between multiple steps or units, which may reduce the amount ofwater required for solvent reduction. For example, an extraction methodor system may include two steps or tanks. Additionally, an extractionmethod or system may include a cross flow filtration column, which mayreduce the solvent concentration and concentrate the amount ofmicroparticles in a suspension. Microparticles may then be rinsed withan inorganic base and dried. This method or system may providemicroparticles with low solvent concentrations and superiorcharacteristics for administering to a patient.

Embodiments of the present technology may include a method for reducinga solvent concentration in a plurality of microparticles. The method mayinvolve contacting a mixture including the plurality of microparticlesand the solvent with water, and this contact may form an aqueoussuspension. A first portion of the solvent may dissolve into the waterof the aqueous suspension to reduce the solvent concentration in theplurality of microparticles from a first solvent concentration in themixture to a second solvent concentration in the aqueous suspension. Themethod may also include transferring the aqueous suspension to aconcentration unit that may further reduce the solvent concentration inthe plurality of microparticles from the second solvent concentration toa third solvent concentration. The reduction to the third solventconcentration may include introducing additional water to the aqueoussuspension in the concentration unit. The reduction may also includeremoving at least a portion of the water and at least a portion of thesolvent from the aqueous suspension in the concentration unit. In theconcentration unit, additional water may be introduced at a slower ratethan the water and the solvent are removed from the concentration unitto form a microparticle concentrate with the third solventconcentration. The method may further include transferring themicroparticle concentrate to a washing unit, where the microparticleconcentrate may be contacted with a washing solution to form an amalgamof washed microparticles with a fourth solvent concentration. The methodmay also include drying the amalgam of washed microparticles to form theplurality of microparticles with a reduced solvent concentration. Theseoperations may work together to reduce the solvent concentration in themicroparticles from the first solvent concentration to the reducedsolvent concentration.

Embodiments may also include a system for reducing a solventconcentration in a plurality of microparticles. The system may include asolvent extraction tank. In the solvent extraction tank, a mixtureincluding the plurality of microparticles and the solvent may becontacted with water to form an aqueous suspension. A first portion ofthe solvent may dissolve into the water of the aqueous suspension toreduce the solvent concentration in the plurality of microparticles froma first solvent concentration in the mixture to a second solventconcentration in the aqueous suspension. The system may also include aconcentration unit in fluid communication with the solvent extractiontank. The concentration unit may further reduce the solventconcentration in the plurality of microparticles from the second solventconcentration to a third solvent concentration. This reduction mayinclude introducing additional water to the aqueous suspension in theconcentration unit. The reduction may also include removing at least aportion of the water and at least a portion of the solvent from theaqueous suspension in the concentration unit. The additional water maybe introduced at a slower rate than the water and the solvent areremoved from the concentration unit. A microparticle concentrate withthe third solvent concentration may be formed. The system may furtherinclude a washing unit adapted to receive the microparticleconcentration from the concentration unit. In the washing unit, themicroparticle concentrate may be contacted with a washing solution andmay form an amalgam of washed particles with a fourth solventconcentration.

Embodiments may further include a method of preparing a plurality ofbiodegradable microspheres with a medically active agent, where thebiodegradable microspheres have a reduced level of a preparationsolvent. The method may include contacting a mixture including theplurality of biodegradable microspheres and the preparation solvent withwater, which may form an aqueous suspension. A first portion of thepreparation solvent may dissolve into the water of the aqueoussuspension and may reduce the solvent concentration in the plurality ofbiodegradable microspheres from a first solvent concentration in themixture to a second solvent concentration in the aqueous suspension. Themethod may also include transferring the aqueous suspension to aconcentration unit that further reduces the solvent concentration in theplurality of biodegradable microspheres from the second solventconcentration to a third solvent concentration. This reduction mayinclude introducing additional water to the aqueous suspension in theconcentration unit. The reduction may also include removing at least aportion of the water and at least a portion of the preparation solventfrom the aqueous suspension in the concentration unit. The additionalwater may be introduced at a slower rate than the water and the solventare removed from the concentration unit to form a biodegradablemicrosphere concentrate with the third solvent concentration. The methodmay further include transferring the biodegradable microsphereconcentrate to a washing unit, where the biodegradable microsphereconcentrate is contacted with a washing solution to form an amalgam ofwashed biodegradable microspheres with a fourth solvent concentration.The method may also include drying the amalgam of washed biodegradablemicrospheres to form the plurality of biodegradable microspheres with areduced solvent concentration. These operations may work together toreduce the solvent concentration from the first solvent concentration inthe mixture to the reduced solvent concentration in the plurality ofbiodegradable microspheres.

Embodiments may also include a composition that can be dried with avacuum unit into a powder for filling a syringe. The composition mayinclude a plurality of biodegradable microspheres, where the pluralityof biodegradable microspheres may include a medically activated agent.In these or other embodiments, the composition may also include asolvent at a concentration of 0.03 wt. % or less. The composition mayfurther include a washing solution that includes an inorganic base. Theinorganic base may have a concentration of 0.1 to 1 w/w %.

Biodegradable microspheres may be loaded into a vial before being mixedwith a diluent and administered to a patient. Repeatable, controlledloadings for medical treatment may may result from biodegradablemicrospheres that are dry, are in powder form, have good flowability,and have a low impurity content. The methods and systems of the presenttechnology may produce a microsphere powder with good flowabilitycharacteristics. The solvent extraction steps may remove impuritiesbelow regulated levels, and the method may include a drying process toremove water from the microspheres. Superior flowability may be achievedthrough reducing microsphere clumping and aggregation by rinsing themicrospheres with an inorganic base.

Additionally, any process to produce flowable, injectable, andsyringeable biodegradable microspheres should be efficient and minimizedegradation of the medically active agent. The combination of solventextraction and drying steps reduces the amount of water needed to beadded to the microspheres to extract the solvent. Reducing water usagereduces input and utility costs and also reduces waste. At the sametime, methods and systems of the present technology may also reduceprocessing time and temperature, which may reduce degradation of themedically active agent or microparticles. Embodiments of the presenttechnology provide these and additional benefits.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present technology are described in conjunction withthe appended figures:

FIG. 1 shows a method for reducing a solvent concentration in aplurality of microparticles according to embodiments;

FIG. 2 shows a process flow diagram of a system for reducing a solventconcentration in a plurality of microparticles according to embodiments;

FIG. 3 shows a method of preparing a plurality of biodegradablemicrospheres according to embodiments; and

FIGS. 4A and 4B show scanning electron microscope (SEM) images of driedmicrospheres not treated and treated with a sodium bicarbonate solution.

DETAILED DESCRIPTION

Conventional methods for extracting solvent from medicinal microspherestypically include using high temperatures to evaporate out the solvent.Applying heat, however, may degrade the microsphere or the medicallyactive agent. Applying heat may also generate solvent fumes, and thesefumes may be harmful to human health and subject to emissionsregulations.

The solvent can also be removed by extracting it from the microsphereswith water. Slightly polar solvents are slightly soluble in water. Forinstance, methylene chloride is slightly polar and is slightly solublein water. Furthermore, the partition coefficient (i.e., the ratio of theconcentration of the solvent in the microspheres to the concentration ofthe solvent in water) is normally a constant at constant temperature.Methylene chloride, for example, has a partition coefficient of about 18at room temperature (i.e., 20° C.). Consequently, a solvent could beremoved from microspheres to below a requisite level in one step with asufficient volume of water. However if the initial concentration ofmethylene chloride was 15% and was reduced in one step to the 300 ppmconcentration considered safe for human injection, almost 9,000 L ofwater per liter of a microsphere suspension would be required. Dividingup the extraction process into multiple steps would decrease the amountof water required but also increase the number of unit operations, suchas vessels and pumps. Extraction in a plug flow reactor, such as in across-flow filtration (CFF) column, would reduce the number of unitoperations but would increase the residence time needed to complete theextraction. Increasing the residence time may degrade the microspheresor the medically active agents. In short, extracting the solvent maylead to tradeoffs between the amount of water, the number of unitoperations, and/or the residence time for the extraction. The presenttechnology provides a balance between these tradeoffs while producingmicroparticles with superior characteristics.

As shown in FIG. 1, embodiments may include a method 100 for reducing asolvent concentration in a plurality of microparticles. Themicroparticles may include biodegradable microspheres that contain amedically active agent. For example, the medically active agent mayinclude a protein, such as insulin or glucagon-like peptide 1 (GLP-1)protein, that is medically active in a patient's body. Other medicallyactive agents include, but are not limited to, insulin analogs (i.e.,insulin with one or several amino acids replaced by other amino acids),peptide hormones, insulin derivatives (i.e., insulin conjugated tocarrier proteins, such as antibodies, antibody fragments, biopolymers,etc.), polynucleotides and their derivatives, polynucleosides and theirderivatives, small molecule therapeutics that are hydrophobic oramphiphilic, biologics, proteins, peptides, and mixtures thereof.

When the microspheres are subcutaneously injected into a patient, themedically active agent is gradually released by the dissolvingmicrospheres. The gradual release of the medically active agent canincrease the time between injections, resulting in a lower injectionfrequency. When the medically active agent includes insulin, the insulinmay be PEGylated by covalently attaching polyethylene glycol units tocertain reactive amino groups on the insulin. PEGylated insulin isdescribed in U.S. application Ser. No. 10/553,570, which is incorporatedherein by reference. In addition, the biodegradable microspheres mayinclude poly(lactic-co-glycolic) acid (PLGA). PLGA is an FDA-approvedpolymer for administration into the human body. PLGA may degrade intolactic acid and glycolic acid, both of which can be safely metabolizedby the human body. In some embodiments, the solvent in themicroparticles may include a halogenated organic solvent. For instance,the halogenated organic solvent may include methylene chloride.

The microspheres may include a plurality of medically active agents. Theplurality of medically active agents may include drugs, proteins, andother compounds in embodiments. A single microsphere may include theplurality of medically active agents. Alternatively, a first pluralityof microspheres may include a first medically active agent, and a secondplurality of microspheres may include a second medically active agent. Athird plurality of microspheres may include a third medically activeagent, and so on. The total amount of the first medically active agentmay be the same as the total amount of the second medically activeagent, whether or not each medically active agent is present in the samemicrosphere. The total amount of the first medically active agent may bedifferent than the total amount of the second medically active agent,whether or not each medically active agent is present in the samemicrosphere. Each medically active agent may have the same or differentrelease times. The microspheres may include microspheres made fromdifferent biodegradable materials.

Method 100 may involve contacting a mixture including the plurality ofmicroparticles and the solvent with water and may form an aqueoussuspension 102. Forming the aqueous suspension may harden themicroparticles so as to reduce the amount of the medically active agentthat may otherwise dissolve into the water of the aqueous suspension. Afirst portion of the solvent may dissolve or be extracted into the waterof the aqueous suspension to reduce the solvent concentration in theplurality of microparticles from a first solvent concentration in themixture to a second solvent concentration in the aqueous suspension. Thefirst solvent concentration in the mixture may be between 1 and 50 wt.%, between 5 and 25 wt. %, or between 10 and 20 wt. % (e.g., 15 wt. %).The second solvent concentration in the suspension may be between 1 and10 wt. %, between 1 and 5 wt. %, or about 2 wt. %.

Along with contacting the microparticle mixture with water, method 100may include transferring the aqueous suspension to a concentration unit104 that may further reduce the solvent concentration in the pluralityof microparticles from the second solvent concentration to a thirdsolvent concentration. In some embodiments, the concentration unit mayinclude a cross-flow filtration unit that may remove water and thesolvent from the concentration unit without removing the microparticles.The reduction to the third solvent concentration may include introducingadditional water to the aqueous suspension in the concentration unit.The reduction may also include removing at least a portion of the waterand at least a portion of the solvent from the aqueous suspension in theconcentration unit. In the concentration unit, additional water may beintroduced at a slower rate than the water and the solvent are removedfrom the concentration unit to form a microparticle concentrate with athird solvent concentration. The third solvent concentration in themicroparticle concentrate may be about 0.5 wt. %. The microparticleconcentrate may include about 1 vol. % or more of the microspheres.

In embodiments, method 100 may further include transferring themicroparticle concentrate to a washing unit 106, where the microparticleconcentrate may be contacted with a washing solution to form an amalgamof washed microparticles with a fourth solvent concentration. The fourthsolvent concentration in the amalgam of washed microparticles may lessthan or equal to 1 wt. %, less than or equal to 0.1 wt. %, or be lessthan or equal to 0.03 wt. % (i.e., 300 ppm). The washing solution mayinclude an inorganic base. This inorganic base may include hydroxides orcarbonates. For instance, the inorganic base may be sodium hydroxide orsodium bicarbonate. The concentration of the inorganic base may be from0.1 to 10 w/w % or from 0.1 to 1.0 w/w %. Without intending to be boundby a particular theory, adding an inorganic base to the microsphere isbelieved to deprotonate molecules on the microspheres and leave themicrospheres with a negative charge. The negatively charged microspheresmay provide a repulsive force that counteracts the attractive forcesthat favor agglomeration of the microspheres.

The washing unit may also separate a first group of microparticleshaving a target diameter from a second group of microparticles having asize outside the target diameter. The target diameter may range from 10μm to 90 μm, 20 μm to 70 μm, or 25 μm to 63 μm according to embodiments.The mean diameter of the microparticles may be between 30 μm and 50 μm,between 30 μm and 40 μm, or about 38 μm. The separation of the firstgroup from the second group may include the stack of porous screens inthe washing unit. The microparticles may include some particles withdiameters smaller than the lower target diameter of 25 μm, depending onthe efficiency of the separation. Microparticles with diameters smallerthan the lower target diameter may total less than 5 vol. %, less than 2vol. %, or less than 1 vol. % of the total number of microparticles.

Additionally, method 100 may include drying the amalgam of washedmicroparticles 108 and may form the plurality of microparticles with areduced solvent concentration. The reduced solvent concentration may beless than or equal to the fourth solvent concentration. A higher amountof solvent in the microparticles at the beginning of the dryingoperation may be more likely to result in aggregated microparticles inthe dryer. Therefore, most solvent concentration reduction should occurbefore drying. These operations of method 100 may work together toreduce the solvent concentration from the first solvent concentration tothe reduced solvent concentration.

Embodiments may also include a system for reducing a solventconcentration in a plurality of microparticles. FIG. 2 shows an examplesystem 200. A water phase mix tank 202, oil phase mix tank 204, andemulsifier 206 produce microparticles or microspheres. Microparticles ormicrospheres may be produced by other means as well and may be any ofthe microparticles or microspheres discussed in this specification.Similarly, the solvent may be any solvent described herein.

The microparticles may be added to solvent extraction tank 208. Insolvent extraction tank 208, a mixture including the plurality ofmicroparticles and the solvent may be contacted with water to form anaqueous suspension. Solvent extraction tank 208 may include a mixer tokeep the microparticles in the aqueous solution from settling to thebottom of solvent extraction tank 208. The mixing speed may be decreasedto minimize foam formation. The water may come from an extraction watertank 210. A first portion of the solvent may dissolve or be extractedinto the water of the aqueous suspension to reduce the solventconcentration in the plurality of microparticles from a first solventconcentration in the mixture to a second solvent concentration in theaqueous suspension.

System 200 may also include a concentration unit in fluid communicationwith solvent extraction tank 208. The concentration unit may furtherreduce the solvent concentration in the plurality of microparticles fromthe second solvent concentration to a third solvent concentration. Thisreduction may include introducing additional water to the aqueoussuspension in the concentration unit. The reduction may also includeremoving at least a portion of the water and at least a portion of thesolvent from the aqueous suspension in the concentration unit. Theadditional water may be introduced at a slower rate than the water andthe solvent are removed from the concentration unit. A microparticleconcentrate with the third solvent concentration may be formed.

The concentration unit may include a cross-flow filtration column 220 influid communication with a second solvent extraction tank 212.Cross-flow filtration column 220 may remove a portion of the water and aportion the solvent from the second solvent extraction tank 212 withoutremoving the microparticles. The waste stream may include solvent at aconcentration in the water that would be low enough to go to aconventional wastewater treatment facility. For instance, the wastestream may include about 1.7% of methylene chloride or between 0.03% and1.4% methylene chloride. Often, wastewater treatment facility limits arebased on absolute amounts and not concentrations. With processing atlarge scales, the solvent may be collected onto activated charcoal beds,which may then be transported to a recycling site.

System 200 may further include a washing unit adapted to receive themicroparticle concentration from the concentration unit. In the washingunit, the microparticle concentrate may be contacted with a washingsolution and may form an amalgam of washed particles with a fourthsolvent concentration. The washing solution may be any washing solutiondescribed herein. The washing unit may include a stack of porousscreens, which may separate a first group of microparticles having atarget diameter from a second group of microparticles having a sizeoutside the target diameter. The target diameter may be any targetdiameter discussed herein.

The washing unit may also include a vacuum unit 214 to evaporate thewater and the solvent from the amalgam washed microparticles to formdried microparticles with a reduced solvent concentration. The washingunit may further include a dry gas supply to carry vapor of the waterand the solvent to vacuum unit 214. The dry gas supply may include, forexample, dry nitrogen gas, an inert gas, or a gas or mixture of gasessubstantially without oxygen. System 200 may also include a product bin216 to receive the dried microparticles with the reduced solventconcentration. In these or other embodiments, system 200 may furtherinclude a drying unit adapted to receive the amalgam of washedmicroparticles from the washing unit a dry the amalgam to form driedmicroparticles with a reduced solvent concentration. The solventconcentrations in system 200 may be the same or different concentrationsas the solvent concentrations discussed herein.

FIG. 3 shows an example of a method 300 of preparing a plurality ofbiodegradable microspheres with a medically active agent, where thebiodegradable microspheres have a reduced level of a preparationsolvent. The microspheres, medically active agent, and the preparationsolvent may be any discussed herein. Method 300 may include contacting amixture including the plurality of biodegradable microspheres and thepreparation solvent with water, which may form an aqueous suspension302. A first portion of the preparation solvent may dissolve into thewater of the aqueous suspension and may reduce the solvent concentrationin the plurality of biodegradable microspheres from a first solventconcentration in the mixture to a second solvent concentration in theaqueous suspension.

Additionally, method 300 may include transferring the aqueous suspensionto a concentration unit 304 that further reduces the solventconcentration in the plurality of biodegradable microspheres from thesecond solvent concentration to a third solvent concentration. Thisreduction may include introducing additional water to the aqueoussuspension in the concentration unit. The reduction may also includeremoving at least a portion of the water and at least a portion of thepreparation solvent from the aqueous suspension in the concentrationunit. The additional water may be introduced at a slower rate than thewater and the solvent are removed from the concentration unit to form abiodegradable microsphere concentrate with the third solventconcentration.

Furthermore, method 300 may include transferring the biodegradablemicrosphere concentrate to a washing unit 306, where the biodegradablemicrosphere concentrate is contacted with a washing solution to form anamalgam of washed biodegradable microspheres with a fourth solventconcentration. The first, second, third, and fourth solventconcentrations may be the same or different as the concentrationsdescribed herein. Likewise, the washing solution may be any washingsolution discussed herein.

Method 300 may also include drying the amalgam washed biodegradablemicrospheres 308 to form the plurality of biodegradable microsphereswith a reduced solvent concentration. These operations may work togetherto reduce the solvent concentration from the first solvent concentrationin the mixture to the reduced solvent concentration in the plurality ofbiodegradable microspheres.

Embodiments may also include a composition that can be dried with avacuum unit into a powder for filling a syringe. The composition mayinclude a plurality of biodegradable microspheres, where the pluralityof biodegradable microspheres may include a medically activated agent.In these or other embodiments, the composition may also include asolvent (e.g., methylene chloride) at a concentration of 0.03 wt. % orless or any concentration discussed herein. The composition may furtherinclude a washing solution that includes an inorganic base. Theinorganic base may have a concentration of 0.1 to 1 w/w % or anyconcentration discussed herein. The microspheres, medically activatedagent, solvent, washing solution, and inorganic base may be the same aswhat has been previously described herein. The composition may furtherinclude nitrogen gas, an inert gas, or any gas or mixture of gasessubstantially devoid of oxygen. The composition may be present in awashing unit or a dryer.

The powder of dried microspheres may be filled into a vial, syringe, orother container. The powder may then be mixed with a carrier liquid toform an injectable suspension that can be injected by syringe into apatient. The powder and the carrier liquid may be mixed just prior toinjection. The powder and the carrier liquid may each be in one barrelof a dual barrel syringe, or they may be in a single barrel of a singlebarrel syringe. The carrier liquid may be a biocompatible liquid, whichmay include water. This carrier liquid may be isotonic and reduce damageto tissues near the injection site. The carrier liquid may include waterand may include preservatives. These preservatives may prevent or reducemicrobial growth and the also maintain microsphere suspension over theperiod of time associated with its potential use. The carrier liquid maynot affect the release kinetics of the microspheres. Furthermore, thecarrier liquid may include a surfactant, which may allow themicrospheres to disperse more readily. The carrier liquid may wet themicrospheres, which include infiltrating pores at the surface of themicrospheres. The wetted microspheres may then be injected in a patient,where they degrade and gradually release a medically active agent. Afterthe medically active agent is released, another dose of wettedmicrospheres may be injected again into the patient at some duration.This duration may be a week or longer than a week.

EXAMPLE 1

With returning reference to FIG. 2, an emulsion of microspherescontaining PEGylated insulin was produced with water phase mix tank 202,oil phase mix tank 204, and emulsifier 206. The ratio of the water phaseto the oil phase varied from 1:1 to 2.5:1. For the emulsion with a 1:1ratio of water phase to oil phase, the methylene chloride concentrationwas 50%. For the emulsion with a 2.5:1 ratio, the methylene chlorideconcentration was 28%. The emulsion was sent to the primary extractiontank 208, where it was mixed continuously with sterile filteredextraction water from an extraction water tank 210 at a ratio of 5.6 Lextraction water per liter of emulsion as it entered the tank. Primaryextraction tank 208 was mixed to maintain a homogeneous suspensionduring the primary and secondary extraction steps.

The primary extraction suspension was pumped from primary extractiontank 208 to secondary extraction tank 212 at a flow rate of 0.25 L/min.The primary extraction suspension was combined in-line with additionalextraction water at a ratio of 4.8 L extraction water per liter primaryextraction suspension prior to entering secondary extraction tank 212.In secondary extraction tank 212, the microspheres were continuouslybeing concentrated. Secondary extraction tank 212 was mixed to maintaina homogeneous suspension.

As microspheres were added to secondary extraction tank 212, thesuspension was pumped out of the tank through cross-flow filtration(CFF) filter 210 and back into the tank at a flow rate equivalent to alinear velocity of 43 cm/sec through the CFF tubes. Restricting the flowreturning to secondary extraction tank 212 applied pressure to the CFF210. A small fraction of the circulating flow was filtered out throughthe ceramic CFF membrane to waste, while microspheres were retained inthe circulating stream. The flow rate of the waste stream varied from 1L/min to 6.3 L/min. The concentration of the methylene chloride in thewaste stream ranged from 0.03% to 1.4%. The waste stream was sent to amunicipal wastewater system. At the scale of this example and at a scale10-times larger, the waste stream can be disposed in a typical municipalwastewater system. Water was filtered out via CFF 210 at the same rateas water and microspheres were added to the secondary extraction tank,maintaining a constant working volume inside secondary extraction tank212. The microsphere concentration process was continued until allmicrospheres had been added to secondary extraction tank 212.

Concentration was continued without additional feed to reduce theextraction bath volume and to achieve a microsphere concentration of1.0% (feed mass/volume). Once the appropriate volume was reached,freshwater was fed to secondary extraction tank 212 as wastewater wasremoved via CFF 210 at the same rate to maintain a constant volume.Water was exchanged at a rate of 15 minutes per diavolume or fullexchange of the working volume (e.g., 1 L/min for a 15 L workingvolume). Extraction water tank 210 and secondary extraction tank 212were heated from 22° C. to 35° C. for over 60 minutes and held at 35° C.to aid in solvent extraction.

After 8.5 diavolumes of water exchange, feed and filtrate flows werestopped. In order to recover the microspheres from the CFF loop, waterwas fed directly to the loop inlet from extraction water tank 210. Avolume of water equal to twice the CFF system hold-up volume was pumpedthrough the loop and into secondary extraction tank 212 so allmicrospheres were collected in the secondary extraction tank 212. Afterholding the microspheres at 35° C. for one hour to complete solventextraction, the entire bath was cooled to 5° C.

After the microsphere bath reached the final temperature of 5° C., thesecondary extraction suspension was transferred to the SWECO™ vibratoryseparator/dryer 214 by pressurizing secondary extraction tank 212 andloading microspheres into the dryer through a top port. While the dryerwas vibrating, the suspension gravity drains through a scalping, or top,screen with spacing of 63 μm. A product, or bottom, screen catches theremaining microspheres larger than 25 μm, allowing liquid and undersizedmicrospheres to fall through a waste drain.

Aqueous sodium bicarbonate was added in a SWECO™ rinse solution tank 218at a concentration of 0.5% w/w in a minimum volume of 2.2 L per 100 gfeed. The solution was mixed to dissolve the sodium bicarbonate andsimultaneously cooled to 5° C. After the entire secondary extractionbath was fed to the dryer, the dryer's drain was closed. Rinse solutionfrom rinse solution tank 218 was fed to the dryer and held for a minimumof 30 seconds. The rinse solution was drained, the process was repeatedfor a second time.

The dryer was then allowed to drain until only a wet cake remained onthe screens (i.e., no standing liquid). The dryer was then isolated fromany vent and supply lines, and vacuum was pulled via the drain port toevaporate the water from the wet cake. A dry nitrogen purge was fed tothe top of the dryer to displace the water vapor. Vibration wascontinuously present throughout the entire process, including duringloading, rinsing, and drying. After drying, the dryer product plug wasopened, allowing the microspheres to flow into product bin 216.

EXAMPLE 2

Example 1 was repeated with an emulsion of microspheres containingnon-PEGylated insulin instead of PEGylated insulin.

EXAMPLE 3

Example 1 was repeated with an emulsion of microspheres containing GLP-1protein instead of PEGylated insulin.

EXAMPLE 4

Example 1 was repeated with an emulsion containing two differentmedically active agents.

EXAMPLE 5

Microspheres were treated with an aqueous sodium bicarbonate solutionand compared to untreated microspheres. The treated microspheres wererinsed three times with a chilled 0.5% sodium bicarbonate solution. Boththe treated and untreated microspheres were dried for 2.5 hours and thenvibrated in the SWECO™ dryer for 13 hours at atmospheric pressure. Hardclumps of sizes up to 3 mm formed in the untreated microsphere batch, asshown in the SEM image in FIG. 4A. Far fewer and smaller clumps formedin the treated portion, as shown in the SEM image in FIG. 4B. Thisexample shows the reduced aggregation of microspheres after rinsing witha sodium bicarbonate solution.

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. Additionally, a number of well-known processes and elementshave not been described in order to avoid unnecessarily obscuring thepresent invention. Additionally, details of any specific embodiment maynot always be present in variations of that embodiment or may be addedto other embodiments.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neither,or both limits are included in the smaller ranges is also encompassedwithin the invention, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a method” includes aplurality of such methods and reference to “the microsphere” includesreference to one or more microspheres and equivalents thereof known tothose skilled in the art, and so forth. The invention has now beendescribed in detail for the purposes of clarity and understanding.However, it will be appreciated that certain changes and modificationsmay be practice within the scope of the appended claims.

1. A system for reducing a solvent concentration in a plurality ofmicroparticles, the system comprising: a solvent extraction tank where amixture comprising the plurality of microparticles and the solvent arecontacted with water to form an aqueous suspension; wherein a firstportion of the solvent dissolves into the water of the aqueoussuspension to reduce the solvent concentration in the plurality ofmicroparticles from a first solvent concentration in the mixture to asecond solvent concentration in the aqueous suspension; a concentrationunit in fluid communication with the solvent extraction tank, whereinthe concentration unit further reduces the solvent concentration in theplurality of microparticles from the second solvent concentration to athird solvent concentration by: (i) introducing additional water to theaqueous suspension in the concentration unit; and (ii) removing at leasta portion of the water and at least a portion of the solvent from theaqueous suspension in the concentration unit, wherein the additionalwater is introduced at a slower rate than the water and the solvent areremoved from the concentration unit to form a microparticle concentratewith the third solvent concentration; and a washing unit adapted toreceive the microparticle concentrate from the concentration unit,wherein the microparticle concentrate is contacted in the washing unitwith a washing solution to form an amalgam of washed microparticles witha fourth solvent concentration.
 2. The system of claim 1, wherein thesolvent extraction tank comprises a mixer to keep the microparticles inthe aqueous suspension from settling to the bottom of the solventextraction tank.
 3. The system of claim 1, wherein the concentrationunit comprises a cross-flow filtration column in fluid communicationwith a second solvent extraction tank, wherein the cross-flow filtrationcolumn removes the water and the solvent from the second solventextraction tank without removing the microparticles.
 4. The system ofclaim 1, wherein the washing unit comprises a stack of porous screens toseparate a first group of microparticles having a target diameter from asecond group of microparticles having a size outside the targetdiameter.
 5. The system of claim 1, wherein the washing unit furthercomprises a vacuum unit to evaporate the water and the solvent from theamalgam of washed microparticles to form dried microparticles with areduced solvent concentration.
 6. The system of claim 5, wherein thewashing unit further comprises a dry gas supply to carry vapor of thewater and the solvent to the vacuum unit.
 7. The system of claim 5,further comprising a product bin to receive the dried microparticleswith the reduced solvent concentration.
 8. The system of claim 1,wherein the system further comprises a drying unit adapted to receivethe amalgam of washed microparticles from the washing unit and dry theamalgam to form dried microparticles with a reduced solventconcentration.
 9. The system of claim 1, wherein the microparticlescomprise biodegradable microspheres that contain a medically activeagent, and the solvent comprises a halogenated organic solvent.
 10. Thesystem of claim 1, wherein: the first solvent concentration is 10 to 20wt. %; the second solvent concentration is 1 to 5 wt. %; the thirdsolvent concentration is about 0.5 wt. %; and the fourth solventconcentration is 0.03 wt. % or less.
 11. The system of claim 1, whereinthe washing solution comprises sodium bicarbonate.
 12. A system forreducing a solvent concentration in a plurality of microparticles, thesystem comprising: a first solvent extraction tank comprising a mixer,where a mixture comprising the plurality of microparticles and thesolvent are contacted with water to form an aqueous suspension, wherein:a first portion of the solvent dissolves into the water of the aqueoussuspension to reduce the solvent concentration in the plurality ofmicroparticles from a first solvent concentration in the mixture to asecond solvent concentration in the aqueous suspension; a concentrationunit in fluid communication with the first solvent extraction tank,wherein: the concentration unit comprises a cross-flow filtration columnin fluid communication with a second solvent extraction tank, thecross-flow filtration column removes the water and the solvent from thesecond solvent extraction tank without removing the microparticles, theconcentration unit further reduces the solvent concentration in theplurality of microparticles from the second solvent concentration to athird solvent concentration by: (i) introducing additional water to theaqueous suspension in the concentration unit; and (ii) removing at leasta portion of the water from the cross-flow filtration column and atleast a portion of the solvent from the aqueous suspension in theconcentration unit, wherein the additional water is introduced at aslower rate than the water and the solvent are removed from theconcentration unit to form a microparticle concentrate with the thirdsolvent concentration; and a washing unit adapted to receive themicroparticle concentrate from the second solvent extraction tank,wherein the microparticle concentrate is contacted in the washing unitwith a washing solution to form an amalgam of washed microparticles witha fourth solvent concentration.
 13. The system of claim 12, whereinintroducing additional water to the aqueous suspension comprisesintroducing additional water to the second solvent extraction tank andthe cross-flow filtration column.
 14. The system of claim 12, furthercomprising an emulsifier in fluid communication with the first solventextraction tank, wherein the emulsifier is configured to producemicroparticles and feed microparticles into the first solvent extractiontank. 15.-22. (canceled)